Fluorine-containing electrolytes typified by perfluorosulfonic acid membranes have carbon-fluorine bonds, and are thereby chemically very stable. Consequently, they are used as solid polymer electrolyte membranes for a fuel cells and for electrolyzers for water, sodium chloride, and halogen acids. In addition, they are applied to humidity sensors, gas sensitive detectors, and oxygen concentrators by using their proton conductivity.
Such fluorine-containing electrolytes are very expensive, because producing thereof needs special method. In addition, when producing halogen compounds and wasting it, due consideration must be given to a facility for preventing environmental pollution. Demands have therefore been made on proton-conductive polymer electrolytes of non-fluorine base which are inexpensive and environmentally harmless.
Examples of inexpensive solid polymer electrolyte membranes can be found as aromatic hydrocarbon electrolyte membranes including, for example, sulfonated polyether ether ketones, sulfonated polyether sulfones, sulfonated acrylonitrile-butadiene-styrene copolymers, sulfonated polysulfides, and sulfonated polyphenylenes in Japanese Unexamined Patent Application Publication (JP-A) No. Hei 06-93114.
Sulfonated aromatic hydrocarbon electrolyte membranes can be more easily produced at lower cost than fluorine-containing electrolyte membranes typified by Nafion (registered trademark) as the electrolyte membrane produced by Dupont Company. However, they are more liable to deteriorate by oxidation and to undergo desulfonation when used in cells.
Accordingly, the present invention is to provide a polymer electrolyte which is resistant to oxidation-induced deterioration and is highly durable. Another object of the present invention is to provide a polymer electrolyte membrane, a polymer electrolyte membrane/electrode assembly, and a fuel cell using the polymer electrolyte.